Recording of electrical impulses



Dec.` 22, 1942. E. wf KELLoGG 2,365,375

RECORDING 01"' ELECTRICAL IMPULSES Filed June so, 1959 mimmo/amas' Fa. Ha. 1

zwentot 1v Edward: wife Gttorneg Patented Dec.4 22.' 1,942

[hir-ao RECORDING E STATES PATENT FFlcl-z .j

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Edward W. Kellozg. Moorestown, N.' J., assigner to Radio Corporation of America. a corporation oi Delaware Application June 30, 1939, Serial No. N228? 2 claims. ici. 11a-roos) This invention relates to the recording oi electrical impulses such as those oi audio frequency. and has for its principal object the provision of an improved apparatus and method of opera-I tion for producingy variable density push-pull .l

- records of the noise reduction type.

The present invention is related to that of Dimmick U. S. Patent 2,095,317 in that itinvolves utilizationy oi a penumbra shadow. It is similar to that of Dlmmick U. S. Patent 2,095,318 in that it involves the production of a variable density push-pull record of the noiseless type, but differs therefrom with respect to the means whereby the loppositely shaded penumbra shad ows are adjusted transversely of the light slit in accordance with the volume of the sound to be recorded. It involves certain structural features like those disclosed by a copending 'application of Underhill, et al.. Serial No. 210,592, hled May 28, 1938, now U. S. Patent'2,268.097, issued December 30, itil, and Vassigned to the same assignee as the present application.

In accordance with the invention, a light beam oi an intensity varying gradually between opposite beam edges is split into two components which are' oppositely shaded and are vibrated component beams when the is relatively low, and

` Figure 5 is an explanatory diagram relating to l the function oi a reversing prism which forms a part oi the optical system.

The system oi Fig. l. includes a light source it. from which light is projected through a spherical lens il, the aperture of a plate I2, 'a prism it, a cylindrical lens it, and a spherical lens it `to the vibratory reflector IB oi" a galvanometer or other suitable recording device. From' the reilector it an image of thel source It is rehected through a lens il, the light slit itl of a plate it, and a lens 2li to the record il.' uponvwhich the impulses are to be recorded. In the vertical plane, lenses iii and il bring arture ii into sharp focus on the plate I9.

.-,Inte xm. the prism it 'are a xed mask 2i and a movable penumbra masi: 23.' Since the penumbra mask it is not sharply focused on the slit plate lil, it causes a penumbra, or softfedged shadow at the slit it. Als this light of graduated intensity is about zero or rest positions determined by the volume or level of the recorded impulses. To this end, a prism or the like may be arranged to separate and reverse one of the beam components, and the position about which both come ponent beams are vibrated at the light slit of the recorder may be determined by the position of a penumbra mask maintained in a position dependent on the level of the recorded impulses. Thus, when the impulse level is relatively low. the low intensity edges oi the componentbeams are biased to a position relatively close to the light slit, and when the impulse level is relatively high these edges are biased to a position more remote irom the light slit.

The invention will be better understood from* tillseintheiorn'ioia moved up and down across the slit it by the movements of the mirror it, the intensity ofthe light image of the slit on the iilm varies in accordance with the deflections of the galvanometer mirror it. and thus produces a sound record or-the variable density ty. As previously indicated; the mask 23 is biased to apositlon dependent on the amplitude or volume of the lmpdlses to be recorded. this posltidn being dependent on the current ofthe shutter-operating ycoil t4. The reflector it is', of course, vibrated inl' accordance with the electrical impulses applied to the galvanometer-operating ooil 25.'

As has already been explained, theshutter 22 wouldcause the iight applied to the reiiector I6 penumbra shadow which would gradually increase in intensity as the top of. the renector is approached. Buch a shadow vibrating transversely of the slit i8 would produce on the record 2i a single sound track of the variable density type. In'order' to produce a push-pull record. the prism I3 is arrangedto intercept and reverse one side ofthe penumbra shadow. Such a prism, the action 'of which isillustrated in Fig. 5, has the property of reversing or inverting the image of the aperture and shutter vane,.but. also reverses the direction of motion o! the image oi the latter. An equalizlns plate i341 extending from or disposed contiguous to the prism Il, asl shown in Figure I, tts the other half ot the penumbra shadow mey rest positions o: the without mveruonana smeer-vesto equau the impulse amplitude l between the. aperture plate and 2 s intensity or brightness of the two beam parte.

pendent on the current ot the coil 24. They arebiased to positions relatively i'ar away from the slit it when the current oi the coil 24 is high, and are biased to positions relatively close to the slit when the current of this coil is relatively low.

In order that the two components of the pushpull sound track may be readily reproduced, it is desirable that they be slightly spaced from one 'another'. For the purpose of producing this desired spacing, an elongated mask 28 is provvided, located in the optical axis 2! of the system. It will be noted that the/stationary mask 22 has ltsupper edge located at the optical axis 2l, and functions as a stop which prevents the penumbra shadow from moving beyond a certain point which is the optimum position for high modulation. Movement of the shutter 23 above the upper edge of the shutter 22 in response to decrease in the volume of the recorded impulses,-

'of course, functions to shift the penumbra shadows so that the slit illumination is decreased in intensity, as shown in Fig. 4, compared with Fig. 3.

The wiring diagram of Fig. 2 illustrates in schematic form the electrical connections oi' the apparatus. Thus, sound is picked up and con i verted intocorresponding electricalimpulses by a microphone lll, and these corresponding electrical impulses are ampliiled by an amplifier 2| and supplied to the operating coil 2l through which the reflector i6 is vibrated. A part of the output oi.' the ampliiler il is supplied, through an amplifier, a rectier and a iilter, indicated generally at 32, to the coil 24 which determines the position of the penumbra shutter 23.' It should be understood that the amplifier, rectiner and i'llter circuits function to produce in the coil `2 4 a direct current which varies in value in accordance with the envelope of the recorded impulses. Otherwise stated, the current in the coil 24 varies as the volume or amplitude of the recorded impulses, and the stationary mask 22 limits the biasing effect, of this current so that it produces no optical effect beyond a value sufilciently large to move the shutter 23 below the upper edge of the shutter' 22.

I claim as my invention: l. In an electrical. impulse recording apparatus, the combination of means for producingv a single light beam, means for thereafter producing two light beams from said single beam, said second named means including a portion adapted to reverse a part of said single bea'm and another portion adapted to4 transmit the remaining part of said single beam withoutreversal, means for vibrating said two light beams in accordance with the impulses to be recorded, and supplementary means for moving said'two beams in accordance with' the strength o! said impulses.

2. The invention set forth in claim 1 characterized in that said second named means comprises a prism adapted to reverse a light beam transmitted thereby, and a plane light transmitting member contiguous thereto adapted to transmit a light beam without reversal, said prism and plane member being so disposed Arelative to said single light beam that said prism transmits and reverses a part of said single beam while said plane member transmits the remain- 4I in! part o! said single beam without reversal.

EDWARD w. mood. 

